Field of Disclosure
The described embodiments relate to real-time calibration of accelerometers.
Description of the Related Art
An accelerometer measures the vector sum of forces from gravity and linear acceleration, and in the absence of linear acceleration, the accelerometer measures gravity alone. Since all accelerometers include sources of error (e.g., bias offset, sensitivity errors, cross-axis errors and sensor noise errors), the measurements do not exactly match the vector sum of gravity and linear acceleration. This means that even in the absence of linear acceleration, the estimate of the gravity vector likely includes errors directly caused by the sources of error in acceleration measurement.
To account for the sources of errors, accelerometers are typically calibrated during manufacturing. The calibration generally consists of manipulating the accelerometer (or a finished device including the accelerometer) with high precision to known truth reference orientations. However, maneuvering the accelerometer to known truth orientations adds both time and complexity to testing of devices, and accordingly increases the manufacturing cost. In some cases, manufacturers may simply opt to skip accelerometer calibration altogether. Moreover, even if factory calibration occurs for an accelerometer, that calibration is only accurate for a limited duration of time. For example, mechanical stresses, accelerometer age, and temperature can all affect an accelerometer's calibration and thus the accuracy of its measurements, and are not effectively accounted for by an initial factory calibration.